Oil wells and gas wells are typically drilled into the ground by rotating a “drill string” made up of multiple sections (or “joints”) of drill pipe connected end-to-end by means of threaded joints, with a suitable drill bit attached to the bottom of the drill string. The drill string typically incorporates heavier tubular members known as heavyweight pipe or drill collars, positioned between the drill bit and the assembly of pipe sections, in order to increase the vertical load on the drill bit and thus enhance its operational effectiveness. Drilling fluid (or “mud” as it is commonly referred to in the industry) is circulated under pressure downward through the drill string and out through ports in the drill bit, and upward to the surface via the annulus between the drill string and the wellbore.
A typical drill collar is fabricated with a “pin end” having a tapered external (i.e., male) thread, and a “box end” having a tapered internal (i.e., female) thread for mating engagement with the pin end of another drill pipe section or drill collar. As well, each pin end of the drill collar is formed with an annular shoulder adjacent the base of the male thread, and the outer face of each box end of the drill collar is formed with a corresponding annular shoulder. When a drill collar connection is “made up” by threading the pin end of one collar into the box end of another collar, the annular shoulders of the pin end and box end are brought into compressive metal-to-metal contact so as to create a mechanical seal preventing leakage of drilling mud. Because of this important function, the annular shoulders of the pin and box ends of the drill collars may alternatively be referred to as “seal shoulders” or “torque shoulders”, and the contact surface of a torque shoulder may be referred to as a “seal face”.
In order for torque shoulders to serve their sealing function as effectively as possible, the seal faces should ideally be uniformly planar and precisely perpendicular to the longitudinal axis of the drill string, and the seal faces should ideally be very smooth, and free from even minor damage or defects.
It is also customary and highly preferred to chamfer or bevel the outer circumferential edges of the seal faces (typically at an angle of approximately 45 degrees), primarily to protect the seal faces from damage during shipping and handling of the drill collars as well as from impact damage that could otherwise occur in the outer regions of the seal faces after a drill collar assembly has been made up and put into service. Although the angled faces of the bevelled edges do not come into contact with other components and do not have a direct sealing function, these angled faces as well should ideally be smooth and free from defects, for reasons discussed later in this document.
Unfortunately, the seal faces and bevelled edges of drill collars and other oilfield tubular items are commonly damaged due to rough handling, accidental impacts, and other incidents of typical well-drilling operations and the sometimes harsh environments in which these operations are conducted. Even minor damage to a seal face, such as scratches and nicks, can significantly impair the effectiveness of the mechanical seal between mating seal faces, to the point where there is no practical option except to replace the damaged tubular and, if possible, to re-face the damaged tubular to restore the stringent seal face requirements discussed above (to facilitate or enable later re-use in the field). Because of these stringent requirements, re-facing of torque shoulders must be carried out with great precision, and one way to do so is to ship the damaged tubulars to a machine shop at an off-site location. However, that is not an ideal option due to transportation costs and lost field production time, and/or the need to have an on-site stock of replacement tubulars, ready for installation while the damaged tubulars are being re-faced in the shop.
A number of machines have been devised for re-facing damaged tubulars in the field, to avoid the cost and inconvenience of shipping them to a machine shop. One particularly good example of such a machine is disclosed in U.S. Pat. No. 4,149,436 (Blattler), which is incorporated herein by reference, and corresponding Canadian Patent No. 1,080,948. The Blattler machine provides a threaded mandrel adapted to receive either the pin end or box end of a tubular workpiece such as a drill collar, the other end of which is supported by a suitable steady rest or other support means. The mandrel and the workpiece are stationary (i.e., non-rotating) during operation of the machine. A cylindrical shaft coaxially disposed around the mandrel rotates a flange plate onto which a tool holder is mounted, with the tool holder being radially movable toward or away from the longitudinal axis of the shaft (and, in turn, toward or away from the workpiece). Biasing means, in the form of a helical spring, is provided to bias the tool holder inward toward the workpiece axis.
The Blattler machine incorporates a wedge mechanism that engages the tool holder such that longitudinal movement of the wedge relative to the cylindrical shaft and toward the tool holder has the effect of displacing the tool holder radially away from the workpiece axis. As may be best seen in FIG. 2 in U.S. Pat. No. 4,149,436, the Blattler machine includes a collar assembly (85) which coaxially surrounds and rotates with a hollow shaft (48), which in turn is coaxially disposed around a non-rotating adapter (14) to which a tubular workpiece may be mounted. The collar (85) is axially slidable relative to the adapter and the rotary tool head (60), which is not axially movable relative to the adapter. A first wedge mechanism component (“wedging member 95”) is mounted in association with the sliding collar (85), and a second wedge mechanism component (“actuating arm 84”) is mounted to a tool holder (62), which in turn is mounted to the rotary tool head (60) so as to be radially movable relative thereto. The actuating arm (84) extends over and engages a sloping surface of the wedging member (95) such that axial movement of the collar (85) toward the rotary tool head (60) will cause radially outward movement of the actuating arm (84) and, in turn, the tool holder (62), and vice versa.
This apparatus is typically set up in an initial position such that a cutting tool mounted to the tool holder is positioned radially clear of the workpiece but longitudinally positioned to cut a desired depth into the torque shoulder of the mounted end of the workpiece. The cylindrical shaft is then rotated, thus also rotating the faceplate and the tool holder about the non-rotating workpiece. The wedge mechanism can then be gradually withdrawn longitudinally away from the workpiece, such that the rotating cutting tool progresses radially inward and machines a new seal face, removing any previously existing damage or defects.
In order to re-face the bevelled edge of the torque shoulder, a separate tool holder is mounted to the flange plate of the machine, with a bevelling tool having a cutting edge oriented to match the desired bevel angle. The radial position of this separate tool holder is pre-set and does not change during re-facing of the torque shoulder edge. With the seal face re-facing tool positioned away from the workpiece (by suitable manipulation of the previously-discussed wedge mechanism), and with the bevelling tool radially positioned for alignment with the torque shoulder edge, the rotating cylindrical shaft is moved longitudinally, over the stationary mandrel, toward the workpiece, such that the bevelling tool engages and re-faces the bevelled edge of the torque shoulder.
In accordance with the operational principles described above, the Blattler machine re-faces the face of the torque shoulder by moving the corresponding cutting tool across and parallel to the seal face, which facilitates the production of a suitably smooth machined surface. However, re-facing of the bevelled edge of the torque shoulder is accomplished by what may be referred to as a plunge cut, meaning that the cutting tool is plunged or forced against and into the workpiece. This process is not conducive to production of an optimally smooth machined bevel surface. Using this process, the cutting tool is susceptible to intermittently catching or bouncing on the workpiece surface due to factors such as mandrel flex or “backlash” resulting from an excessive plunge rate. This can cause what is commonly referred to in machining parlance as “chatter”, which in turn causes the cutting tool to create gouges or other defects in the bevel surface. Such defects in the bevel surface are highly undesirable, particularly because if they occur near the inner perimeter of the bevel surface they can also create unacceptable defects in the seal face. In that event, re-facing of the seal face may have to be repeated.
It is clearly desirable, therefore, to re-face the bevel edges of torque shoulders using means that do not involve “plunging” motion of the cutting tool, in order to avoid chatter and resultant workpiece damage. Ideally, this operation would be carried out by moving a cutting tool across and parallel to the bevel face, in a manner analogous to the re-facing of torque shoulders as accomplished using the Blattler machine. Unfortunately, the Blattler machine as disclosed in U.S. Pat. No. 4,149,436 cannot carry out this mode of operation, and it is apparent that there are no other known machines or apparatus that are capable of re-facing the bevel edge of a torque shoulder in this desirable fashion.
Accordingly, there is a need for methods and apparatus for machining or re-facing a circumferential bevel edge on the end of a tubular member using a cutting tool that moves across and parallel to the face of the bevel. There is a further need for apparatus that is capable of carrying out such a bevel re-facing operation and is also adaptable for retrofitting onto re-facing machines that provide for only radial movement of the cutting tool relative to a tubular workpiece.